SEVARE, Mali -- Islamic extremists based in the Malian town of Ansongo have destroyed a bridge near the Niger border, officials said on Friday, marking the first use of explosives by the insurgents since the start of a French-led military intervention two weeks ago.

The explosion shows that the extremists remain a nimble and daunting enemy, despite gains by the French, who have recaptured three towns from the insurgents and on Friday pushed toward the Islamist stronghold of Gao, one of three provincial capitals controlled by the al-Qaida-linked rebels.

Djibril Diallo, the village chief of Fafa, located 12 miles (20 kilometres) from the bridge, said by telephone on Friday that residents of his town had called him to confirm that members of the Movement for the Oneness and Jihad in West Africa had travelled toward the border with Niger to the outskirts of Tassiga on Thursday, before destroying the bridge crossing into the town. The rebel group, also known as MUJAO, travelled from the locality of Ansongo, roughly 25 miles (40 kilometres) from Tassiga.

"That's exactly right. They exploded it. It was last night at around 9 p.m. The Islamists left their barracks in Ansongo after the airstrikes, and headed toward Niger. They caused the collapse of the bridge near the town of Tassiga, not far from Niger," said Diallo.

Julie Damond, a spokeswoman with aid group Doctors Without Borders, which has a team in Ansongo, said no injuries were directly related to the explosion. However, several people were being treated in the Ansongo hospital after a bus they were riding in fell into a hole in the bridge caused by the blast, she told The Associated Press by telephone from Bamako, the Malian capital.

The attack recalls insurgent tactics used in Iraq and Afghanistan. It appeared aimed at stopping the advance of African troops, stationed in neighbouring Niger, who are expected to travel by road into Mali past Tassiga in order to retake the strategic town of Gao. However, the bridge is not the only way to cross the body of water, said Ibrahim Ag Idbaltanate, a former deputy in Mali's parliament from the district where Tassiga is located.

"It's a bridge that is especially used to cross the canyon during the rainy season, when there is a lot of water. But you can make a detour of 3 to 6 miles (5 to 10 kilometres) and find another way to continue on the Niger-Gao road," he said.

However, the bombing of the bridge in Tassiga should cause concern about the strategic bridge leading into the city of Gao itself, said several officials.

An elected official from northern Mali, who spoke on condition of anonymity because he feared reprisal, said that fighters belonging to MUJAO were seen on the bridge leading to Gao overnight, and there were reports that they planned to bomb it. They then abandoned the idea.

"Their intention was to dynamite it. But finally they decided not to. I don't know why they abandoned their plan to do so," the official said.

Despite these setbacks, Mali's military and French forces pushed toward Gao on Friday, in their farthest move north and east since launching an operation two weeks ago to retake land controlled by the rebels, residents and a security official said Friday. The soldiers were seen in the town of Hombori, according to residents, who said they stayed several hours in the area before heading back westward.

"They were in eight all-terrain vehicles and two armoured vehicles," said Maouloud Daou, a resident of Hombori. "They asked us if there were Islamists in the town and we told them they had left. People were very happy to see the Malian and French military."

A Malian security official, who spoke on condition of anonymity because he was not authorized to speak to journalists, confirmed the advance.

Hombori is located 93 miles (150 kilometres) beyond the current line of control in Douentza, which came back under government forces earlier in the week. The northeastward push puts them just 155 miles (250 kilometres) away from Gao, one of the three main northern cities held by Islamists since last April when the rebels took advantage of the chaotic aftermath of a coup in Mali's capital to seize Mali's northern half, an area larger than Afghanistan.

Since France began its military operation two weeks ago with a barrage of airstrikes followed by a land assault, the Islamists have retreated from three cities in Central Mali, including Diabaly, Konna and Douentza. The Islamists still control the majority of the territory in Mali's north, most importantly the three provincial capitals in the north, including Gao, Kidal and Timbuktu.

The French currently have some 2,400 forces in the country and have said that they will stay as long as needed in Mali, a former French colony. However, they have called for African nations to take the lead in fortifying the Malian army's efforts. There are currently some 1,750 troops from countries in the region, including Togo, Nigeria, Burkina Faso, Benin, Senegal, Niger and Chad.

Britain's Ministry of Defence on Friday said it was deploying a spy plane, a Sentinel R-1 aircraft, to Mali to help with the military intervention. The specially modified jet's radar can be used to hunt ground targets. Britain already has deployed two C-17 cargo planes to aid the offensive.

On Friday, the head of the European Union's planned military training mission to Mali briefed officials on his reconnaissance mission to Bamako. He told them that, despite the rapidly evolving conditions on the ground, the training mission is needed more than ever, according to Sebastien Brabant, a spokesman for EU foreign policy chief Catherine Ashton.

French Brig. Gen Francois Lecointre told the officials in Brussels the mission is welcomed by the Malian armed forces and will be instrumental in building a Malian army which can be a sustainable, democratic tool under civilian authority, Brabant said.

The launch of the training mission is expected by mid-February, subject to a decision by the council of EU foreign ministers. Training activities could start a few weeks after that, the spokesman said.